1. Field of the Invention
This invention relates to a rotating head type reproducing apparatus and more particularly to an apparatus arranged to reproduce a recorded signal by tracing, one after another, with rotating heads many recording tracks formed on a record bearing medium at a given track pitch.
2. Description of the Prior Art
The known rotating head type video signal reproducing apparatus include magnetic recording and/or reproducing apparatus of the kind arranged to record a video signal forming oblique recording tracks on a magnetic tape and to reproduce the recorded signal with two rotating heads (hereinafter will be called VTR for short). In this specification, the invention will be described, by way of example, as applied to a VTR.
A high density recording tendency of VTR's of recent years calls for tracing the recording tracks with fidelity. To meet this requirement many varied tracking methods have been contrived for accurately correcting the deviation of a reproducing head from the recording tracks (hereinafter referred to as a tracking error). In one of the prior art tracking methods, four pilot signals of different frequencies are superimposed on one-field portions of a video signal one after another during recording. Then, during reproduction, the pilot signals are reproduced from a reproducing track which is mainly traced by a head (hereinafter referred to as the main track) and also from adjacent tracks located on both sides of the main track. Tracking is thus carried out utilizing the pilot signals thus reproduced. In accordance with this method, the tracking error is detected by comparing the levels of the pilot signal components reproduced from the two adjacent tracks.
Meanwhile, the applications of VTR's have diversified. VTR's capable of performing special reproducing operations by allowing a magnetic tape to travel at a speed different from a speed employed for recording, such as still picture reproduction, slow motion reproduction, and high speed search reproduction are now increasing. For the special (or varied speed) reproduction of this kind, the reproducing head must be arranged to accurately trace each track without trespassing on other tracks in order to safely obtain a sharply reproduced picture. In one known method for meeting this requirement, a pattern signal generator is arranged to generate a pattern signal corresponding to a distance to a recording track to be reproduced (or reproducing track) on the tape from the scanning locus of a reproducing head obtained at a given tape travel speed. The reproducing head is shifted by some shifting means, such as a piezoelectric conversion element (for example, a bimorph element), in a direction perpendicularly crossing the rotation plane thereof and the shifting means is controlled according to the pattern signal. However, a tracking, error of course, arises even where a noiseless picture is obtained through varied speed reproduction carried out by this method. The conventional tracking method for correcting the tracking error is as follows: During recording, a control signal (hereinafter referred to as CTL signal), which is synchronized with the vertical synchronizing signal, of a video signal is recorded on and along one side of a magnetic tape. During reproduction, the CTL signal is reproduced to detect a relative tracking error and tape moving means such as a capstan, etc. and the above-stated shifting means are controlled based on the result of the error detection. This tracking method, however, takes an excessively long tracking time. Particularly, where the tape travels at a low speed as in the case of slow motion reproduction, a long time interval is required for reproduction of the CTL signal and thus an excessively long time becomes necessary for tracking. Besides, this tracking method is not applicable to still picture reproduction.
In view of this, to obtain tracking error signals without fail, it is conceivable to use the above-stated pilot signals for tracking in varied or special speed reproduction. However, in carrying out varied speed reproduction using the above-stated shifting means in a VTR of this kind, tracking control cannot be performed before the reproducing head actually begins to trace the track due to the absence of the CTL signal. Therefore, at the initial stage of a reproducing operation, the center line of a recording track and the center of the tracing locus of the reproducing rotary head deviate from each other in the travelling direction of the record bearing medium, although they are parallel with each other.
Generally, the capstan is controlled by means of the above-stated CTL signal immediately after commencement of tracing. However, a certain period of time is necessary for following it. It is, therefore, conceivable to add the above-stated CTL signal to the pattern signal in case of varied or special speed reproduction. However, the CTL signal is not obtainable until the reproducing rotary head begins to trace the recording tracks of the tape. Therefore, since the tracing locus of the reproducing head is always deviating in the given direction from the recording track as mentioned above, a tracking operation is necessary for each of the recording tracks to be traced. Then, the operation of the shifting means becomes unstable since the shifting means must be driven by the CTL signal immediately after the start of every tracing action. Beside, since no tracking has been done at the start of tracing, this degrades the quality of a picture thus reproduced.
The details of the conventional VTR of the kind performing the tracking operation with the CTL signal are as follows: Referring first to FIG. 1 of the accompanying drawings, a magnetic tape 1 is employed as a record bearing medium. Reproducing magnetic heads 2A and 2B have the same azimuth angle and are opposed to each other at 180 degrees. These heads 2A, 2B are mounted on the free ends of piezoelectric conversion elements 3A and 3B, such as bimorph elements. The tail ends of the conversion elements 3A and 3B are attached to a rotating member 4. The rotating member 4 is arranged to be rotated by a head rotating motor 5 in the direction of an arrow shown in the drawing. Although it is not shown in the drawing, the heads 2A and 2B are arranged to be rotated while protruding from a slit provided between a pair of tape guide drums in a known manner. Furthermore, the tape 1 is obliquely lapped more than 180 degrees around this pair of drums. A rotation phase detector 6 is arranged to detect the rotation phase of the heads 2A and 2B and to produce a signal which is used as a head switching signal (hereinafter referred to as an HSW signal) and is also supplied to a head motor control circuit 7. The head motor control circuit 7 is arranged to control the head rotating motor 5 via a head motor driving circuit 8 on the basis of the output of the detector 6 in such a way as to rotate the heads 2A and 2B at a predetermined rotation phase and at a predetermined rotational frequency. A control signal reproducing head 9 (hereinafter referred to as the CTL head) is arranged to reproduce a control signal (CTL signal) which is recorded on the lower part of the tape 1 at intervals, each corresponding to one frame portion of the signal to be reproduced, in the longitudinal direction of the tape 1. A capstan 10 is arranged to form a tape moving means for moving the tape 1 in the longitudinal direction thereof in conjunction with a pinch roller which is not shown. A capstan motor 11 is arranged to rotate the capstan 10. A frequency signal generator 12 is arranged to generate a frequency signal (hereinafter referred to as the capstan FG signal) which is representative of the rotation of the capstan 10. A capstan motor control circuit 13 is arranged to control, via a capstan motor driving circuit 14, the capstan motor 11 on the basis of the CTL signal from the CTL head 9 and a capstan FG signal from the frequency signal generator 12 in such a way as to rotate the capstan 10 at a predetermined phase and at a predetermined rotational frequency. A pattern signal generating circuit 15 is arranged to generate a pattern signal on the basis of the HSW signal from the rotation phase detector 6, the CTL signal from the CTL head 9 and the capstan FG signal from the frequency signal generator 12. The pattern signal is applied to the piezoelectric conversion elements 3A and 3B, causing the heads 2A and 2B to trace one and the same recording track on the tape 1 in each scanning field where reproduction is performed at each of arbitrary varied speeds including still picture reproduction and reverse rotation reproduction among others. A conversion element driving circuit 16 is arranged to drive the conversion elements 3A and 3B based on the pattern signal from the pattern signal generating circuit 15.
FIG. 2 shows, by way of example, the details of the above-stated pattern signal generating circuit 15. The circuit 15 is provided with input terminals 17, 18 and 19 which are arranged to receive the capstan FG signal from the frequency signal generator 12, the CTL signal from the CTL head 9 and the HSW signal from the rotation phase detector 6. A binary counter 20 is arranged to count the capstan FG signal which is supplied to the terminal 17 and to be reset by the CTL signal which is supplied to the terminal 18. A timing signal generating circuit 21 is arranged to generate a timing signal on the basis of and in synchronization with the HSW signal supplied to the terminal 19. A presettable binary counter 22 is arranged to be preset by the timing signal from the timing signal generating circuit 21 with the output of the counter 20 used as a presetting data PD and to count the capstan FG signal supplied to the terminal 17. A digital-to-analog (D/A) converter 23 is arranged to D/A convert the output of the presettable counter 22. A still pattern generator 24 is arranged to generate a still picture reproducing fixed pattern signal on the basis cf the timing signal coming from the timing signal generating circuit 21. An adder 25 is arranged to add together, the output of the D/A converter 23 and that of the still pattern generator 24. An output terminal 26 is arranged to produce a conversion element controlling pattern signal which is the output of the adder 25.
The special reproducing operation of the VTR, which is arranged as mentioned above, and particularly the operation of the pattern signal generating circuit 15 of FIG. 2 is described with reference to FIGS. 3 and 4 in the following: In FIG. 3, parts (d)-(g) show the CTL signal, the output of the counter 20 of FIG. 2, the output of the presettable counter 22 or the D/A converter 23 of FIG. 2 and the output of the adder 25 of FIG. 2 respectively obtained at the time of reproduction performed at a speed increased 1.5 times. FIGS. 4(A) and 4(B) show the scanning center loci of the heads 2A and 2B relative to the center loci of recording tracks on the tape 1 obtained respectively during and still picture reproduction and the 1.5 times increased speed reproduction.
With the heads 2A and 2B rotated by the head motor 5, the rotation phase detector 6 produces the HSW signal as shown at a part (a) of FIG. 3. Then, the timing signal generating circuit 21 of the pattern signal generating circuit 15 shown in FIG. 2 produces a timing signal which is synchronized with the rise and fall of the HSW signal, as shown at a part (b) of FIG. 3. In accordance with this timing signal, the still pattern generator 24 produces a still pattern signal for causing the heads 2A and 2B to be continuously shifted from 0 to 1 track pitch (hereinafter referred to as TP) within a scanning range for one field.
In carrying out a so-called field still reproducing operation in which one field signal recorded in one recording track with a recording head having the same azimuth angle as the reproducing heads 2A and 2B is reproduced alternately by means of the two heads 2A and 2B, the relation of the scanning center loci of the heads 2A and 2B to the recording track on the tape 1 becomes as shown in FIG. 4(A). Referring to FIG. 4(A), full lines represent the center loci of the recording tracks of the field signal recorded by the recording head having the same azimuth angle as the reproducing heads 2A and 2B. Broken lines represent the center loci of recording tracks of a field signal recorded by a recording head having an azimuth angle which differs from that of the heads 2A and 2B. An outline arrow represents the scanning center loci of the heads 2A and 2B. A symbol CTL denotes the recording loci of the CTL signal. FIG. 4(B) is also drawn in the same manner. As shown in FIG. 4(A), the scanning center loci "c" of a heads 2A and 2B (hereinafter referred to as the head locus "c") become a line segment diagonally connecting the beginning end of a center locus "a" of the track to be reproduced (hereinafter referred to as the track locus "a") to the terminating end of an adjacent track locus "b" on the left side of the track locus "a". To correct this deviation and to adjust the head locus "c" to the track locus "a", the heads 2A and 2B are continuously shifted from 0 to 1 TP within one field scanning range in a direction reverse to the direction in which the tape 1 travels during recording. In other words, assuming that the tape 1 travels in the direction of "+" during recording, the heads 2A and 2B are shifted in the direction of "-".
It will be understood from the above description that the still pattern signal, which is produced from the still pattern generator 24 as shown at the part (c) in FIG. 3, is capable of satisfying the requirement in shifting the heads 2A and 2B for field still reproduction.
Meanwhile, the capstan FG signal produced from the frequency signal generator 12 with the capstan 10 rotated by the capstan motor 11 is supplied to the counters 20 and 22, which are included in the pattern signal generating circuit 15 of FIG. 2. These counters 20 and 22 count the capstan FG signal. However, since the counter 20 is reset by the CTL signal of the CTL head 9 for every one-frame portion, the upper limit of the counted value of the counter 20 is set at a value corresponding to +2 track pitches. In the event of the 1.5 times increased speed reproduction, since the CTL signal becomes as shown at a part (d) of FIG. 3, the output of the counter 20 becomes as shown at a part (e) of FIG. 3. The presettable counter 22 counts the capstan FG signal while being preset by the timing signal from the timing signal generating circuit 21 (a part (b) of FIG. 3) at the output value of the counter 20 obtained at that time. Therefore, the count output of the counter 22 or the output of the D/A converter 23 becomes as shown at a part (f) of FIG. 3 during the 1.5 times increased speed reproduction. Accordingly, the adder 25 adds up the output of the D/A converter 23 obtained at that time and the output of the still pattern generator 24 and produces a pattern signal as shown at a part (g) of FIG. 3 during the 1.5 times increased speed reproduction.
Since the counters 20 and 22 are arranged to count the capstan FG signal, the outputs cf these counters 20, 22 and the adder 25 include small stepwise variations therein. However, such variations are omitted in the drawing for simplified illustration.
In the event of 1.5 times increased speed reproduction, the head locus in relation to the track locus on the tape 1 becomes as shown in FIG. 4(B). Referring to FIG. 4(B), reference symbols A1, A2, A3,--denote head loci of the head 2A; B1, B2, B3,--denote head loci of the head 2B; and a1, a2, a3,--denote track loci of the field tracks recorded by a recording head having the same azimuth angle as the heads 2A and 2B. For the first field, the head 2A must be continuously shifted to an extent corresponding to a distance from 0 to +0.5 TP within the first field scanning range in order to adjust the head locus A1 to the track locus al. For the second field, the head 2B must be continuously shifted to an extent corresponding to a distance from +1.5 TP to +2 TP within the second field scanning range in order to adjust the head locus B1 to the same track locus al. In the third field, the head 2A must be continuously shifted to an extent corresponding to a distance from +1 TP to 1.5 TP within the third field scanning range in order to adjust the head locus A2 to the track locus a2. In the fourth field, the head 2B must be continuously shifted to an extent corresponding to a distance from +0.5 TP to +1 TP within the fourth field scanning range in order to adjust the head locus B2 to the track locus a3. After that, the above-stated adjustment steps are repeated in a cycle for every four field periods. The pattern signal which is shown at the part (g) in FIG. 3 is appropriate for shifting the heads 2A and 2B in the above-stated manner.
While the 1.5 times increased speed reproducing operation is described by way of example in the foregoing, the pattern signal generating circuit 15 is capable of giving other pattern signals required in controlling the heads 2A and 2B for other reproducing operations to be carried out at desired speeds other than the speed increased 1.5 times.
The pattern signal which is thus obtained from the pattern signal generating circuit 15 is supplied to the conversion element driving circuit 16. Then, the driving circuit 16 drives the piezoelectric conversion elements 3A and 3B to bring the heads 2A and 2B to an applicable reproducing track on the basis of the above-stated pattern signal and the HSW signal from the rotation phase detector 6.
In the conventional apparatus, as described above, the pattern signal is obtained to control the head in a manner suitable for reproduction at a speed selected as desired. However, in accordance with the arrangement of the conventional apparatus, the CTL signal is indispensable for forming the pattern signal and, therefore, the arrangement becomes totally incapable of functioning for a system not using the CTL signal. Furthermore, it is another shortcoming of the conventional apparatus that, in the absence of the CTL signal, the position of the head cannot be controlled in bringing the rotating head onto the magnetic tape 1.
Even if these problems are completely solved, conventional apparatus still have the following problem: Assuming that the travelling speed of the tape 1 for recording is "v" and the tape 1 travel speed for reproduction is Nv (N representing a speed in the positive direction if it is of a positive value and in the negative direction if it is of a negative value), the extent to which a reproducing head 2A, 2B must be shifted during one field period is proportional to a value (N-1) times the TP. This means that, in view of this, the gradient of a fixed pattern signal is arranged to be proportional to (1-N).
Therefore, as will be further described later with reference to the accompanying drawings, in the conventional method for generating the pattern signal, a signal is first formed with a gradient based on the travelling speed of the tape 1 and then a signal representing the difference between them is obtained by forming a symbol representing a gradient of 1/N. However, this method necessitates two wave form forming circuits for forming two wave forms of different gradients and accordingly an arrangement to adjust the timings of the two wave forms. This arrangement thus has often resulted in a complex circuit arrangement.
It is an object of this invention to provide a rotating head type reproducing apparatus which is capable of solving the above-stated problems of the conventional apparatus and which always satisfactorily performs a tracking operation at an arbitrary travelling speed of a record bearing medium.
It is another object of this invention to provide a rotating head type reproducing apparatus which is capable of forming a control signal for shifting the head thereof in the event of reproduction at an arbitrary travelling speed of a record bearing medium without recourse to any special control signal recorded in the travelling direction of the record bearing medium.
It is a further object of this invention to provide a rotating head type reproducing apparatus which is capable of accurately controlling the thrusting position of the rotating head thereof on a record bearing medium.
It is a still further object of this invention to provide a rotating head type reproducing apparatus which permits simplification of a control signal forming circuit arranged to form a control signal for a head shifting operation.
These and further objects and features of this invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.